Journal of Geochemical Exploration最新文献

The Paleoproterozoic is known to host significant sedimentary manganese accumulations deposited in peri-cratonic areas. The depositional environments, the source of Mn and the geometry of the basins are often poorly understood, although they are key aspects in understanding the origin of these strategic resources. We investigate the Mn-rich graphitic metasediments of the Ampanihy district (South Madagascar) to characterize depositional conditions and to identify potential hydrothermal alteration. The results show that the ore is predominantly composed of Mn silicates (spessartine, rhodonite) with accessory jacobsite and pyrophanite varieties rich in Zn close to the Ampanihy shear zone. Geochemical data suggest that the source material in the eastern domain (Ankara) of the district is more crustal in origin than sediments in the western part of the district (Vohidrakitsy, Bekily). The Ankara deposits have chemical characteristics that are close to many other Paleoproterozoic Mn deposits and can be considered as relatively unaltered and fits with the euxinic model. The western domain of the Ampanihy district shows strong hydrothermal overprinting, with significant enrichment in Zn, Ba and Sb, resulting from post-depositional hydrothermal alteration along the proto-Ampanihy shear zone. This event took place at some stage between the deposition of the sediments (c. 1.9‐1.7 Ga) and the suture of the Vohibory and Androyen domains (c. 0.63–0.60 Ma). Based on our data, we propose a new discrimination plot, (La/Lu)_PAAS vs Zn/Ni, which helps in the identification of sediment sources and the recognition of hydrothermal overprinting.

Deep-sea sediments with an abundance bioapatites and Fe–Mn (oxyhydr)oxides in the Pacific Ocean have been considered potential reservoirs of rare earth elements and yttrium (REY). However, comprehensive assessment of the resource potential of REY in deep-sea sediments with Fe–Mn (oxyhydr)oxides throughout the Pacific Ocean is limited due to difficulties in accurately predicting the distribution of extensive Fe–Mn (oxyhydr)oxides and the associated REY. In this study, we predicted the prospective area and resource potential of REY-rich sediments with Fe–Mn (oxyhydr)oxides by considering multiple factors that control REY enrichment based on data from International Ocean Discovery Program (IODP) samples and previous research. According to the distribution map inferred by comprehensively evaluating lithology (clay sediment), hydrothermal fluid influence (δ³He), and water depth (bathymetry), deep-sea sediments with Fe–Mn (oxyhydr)oxides, which have higher than 1000 ppm REY concentration, are distributed in the vicinity of the East Pacific Ridge within a water depth range of 4000–4600 m, and their distribution area is estimated to be approximately 1.1 million km². If the sedimentation rate (<1.5 m/Myr) is considered, which is a crucial factor influencing REY enrichment, we can achieve a more precise assessment of their distribution area. Assuming a recovery depth of only 1 m, the REY resource amount was estimated to be approximately >450 million tons of REY oxide. Even without accounting for REY resource amount associated with bioapatite, the minimum REY resource amount estimated in this study exceed the world's current land reserves. Furthermore, these sediments contain a significant abundance of industrially important heavy REY, accounting for 53 % of REY resources. This implies that the deep-sea sediments with Fe–Mn (oxyhydr)oxides in the Pacific Ocean are a promising resource of REY. Our findings will serve as essential information for the technological progress required in the exploration and development of REY resources in deep-sea sediments in the future.

With a growing demand for the rare earth elements (REE), exploration of regolith-hosted REE resources worldwide has been thriving in recent years and development of a rapid and reliable field-based tool will greatly facilitate the survey and exploration. In this study, we use visible and short-wave infrared (VNIR-SWIR) reflectance spectroscopy to comprehensively evaluate the applicability of the technique to explore regolith-hosted REE resources, exemplified by three representative regolith-hosted REE deposits in China. Neodymium among the REE shows reliably detectable spectral features in the VNIR-SWIR spectroscopy down to concentrations of 10–50 ppm in field samples with heterogeneous mineral grain sizes. The Nd spectral intensity of electronic transition at the band of ∼800 nm is correlated with bulk Nd concentrations and can be used as semi-quantitative indicators for the Nd concentrations, thereby the total REE in regolith. Moreover, VNIR-SWIR spectroscopy is demonstrated to be capable of delineating favorable ore-bearing mineralogy by characterizing the abundance and type of clay minerals and Fe (oxyhydr)oxides, and the crystallinity of kaolinite-group minerals. However, the Nd spectral features of samples with high bulk Fe₂O₃ contents (>3 wt%) are significantly masked due to overlapping by the strong absorption features of ferric (oxyhydr)oxides. VNIR-SWIR spectroscopy is deemed to be applicable to the exploration of regolith-hosted REE resources developed from Fe-poor felsic rocks.

Arsenic (As) and mercury (Hg) are highly toxic contaminants whereas selenium (Se) is both an essential trace element and potentially harmful at higher concentrations. The hyper-saline lakes of southern Bolivian Altiplano, which are ecological niches for endemic species, are also expected to be enriched in these toxic trace elements. The biogeochemistry of As, Hg, and Se in such high-altitude extreme environments (e.g., high UV radiation and salt content) remains poorly understood. In this study, we investigated the concentrations and chemical forms (speciation) of As, Hg, and Se in sediment, water, and air samples of Lagunas Colorada (LC), Verde (LV), and Blanca (LB) in the South Lipez region (>4200 m a.s.l.). We compared them with the repartition of biodiversity (invertebrates, algae, and bacteria). Extreme As concentrations were found in water (up to 82 mg L⁻¹), and the main As species was inorganic As(V), with neither biogenic methylated As nor volatile As forms being detected in water and air, respectively. Se concentrations in water were of 0.1 to 1.4 μg L⁻¹, and Se existed under different redox states, i.e., Se(IV), Se(VI), and reduced Se (0, -II), including biogenic methylated Se(-II) (trimethyl selenonium). Volatile Se compounds (e.g., dimethyl selenide) were detected in water and air samples. Hg was enriched in the surface water (6 to 30 ng L⁻¹) compared to other regional water bodies, and a significant amount of methyl-Hg and gaseous Hg(0) was detected. The drastic disparity between As, Se and Hg concentrations and speciation between lakes has important implications for their cycling in these extreme aquatic systems. While As mostly accumulated in its oxidized and non-volatile form, Hg and Se concentrations can be controlled by significant conversion to reduced and methylated forms, allowing efficient evasion to the atmosphere. Finally, the salinity, including major ions, and high levels of As were among the main drivers of biodiversity repartition between lakes.

The Kumishi area is located in the eastern part of the South Tianshan Orogen, which hosts several gold deposits and has substantial gold discovery potential. The timing of gold mineralization at Kumishi, however, has been poorly constrained owing to the absence of suitable dating minerals. Hydrothermal activity at Wuzunbulake is divided into the pre-ore stage 1 pyrite-quartz, syn-ore stage 2 quartz(-sulfide) and post-ore stage 3 quartz-calcite alteration/mineralization. Three types of pyrite have been recognized, i.e., Py₁ (stage 1), Py₂ (stage 2), and Py_WR (from wallrock). Our in-situ RbSr dating on stage 2 sericite yielded an isochron age of 351.0 ± 17.4 Ma, indicating Early Carboniferous gold mineralization. Py₁ and Py₂ have δ³⁴S_ΣS = 8.28–15.97 ‰ (avg. 12.88 ‰) and 6.92–8.70 ‰ (avg. 7.67 ‰), respectively, indicating that the sulfur in Py₁ was metamorphic fluid sourced, while that of Py₂ may have a mixed metamorphic fluid and wallrock source (0.84–3.27 ‰; avg. 2.31 ‰). For Py₁, its contents of Au, As, Ag, Bi, Co, Cu, Mn, Ni, Pb, Sb, Tl are the lowest. Py₂ has significantly higher Au-As-Ag, slightly higher Co-Cu-Ni-Sb-Tl, but lower Bi-Mn-Pb contents than those in Py_WR. Considering also the sulfur isotope features, we considered that Py₁ was primarily originated from the initial ore-forming fluid, and Py₂ was derived from both the ore fluid and Py_WR, with the former being more important and represents the source of gold. Based on that Py₂ was formed by metasomatism on the Py_WR margin and the element spatial coupling characteristics shown in EPMA geochemical maps, we inferred that the Au enrichment and precipitation are associated with fluid-rock reactions. The initial ore fluid is likely featured by the enrichments in Au, As, Ag, Co, Cu, Ni, Sb, Tl, and depletions in Bi, Mn, and Pb. The Wuzunbulake is best classified as an orogenic gold deposit based on its tectonic background, wallrock alteration style, and the ore-fluid source and characteristics.

The hydrogeochemical signature of the discharged water can reveal significant information on the circulation and evolution of geothermal water, which can further guide the exploration and utilization of geothermal water resources. In this study, the source of major ions, reservoir temperature, and cycle time of geothermal fluids were clarified by the Ion relationship analysis, integrated multicomponent solute geothermometry method, and ¹⁴C isotope analysis, respectively, in the Wugongshan area of South China. Results show that the eastern and western parts of the Wugongshan area have distinct types of geothermal fluids, i.e. HCO₃-Na and SO₄HCO₃-Na, respectively. The major source of HCO₃⁻ and Na⁺ is the hydrolysis of silicate minerals, partially accompanied by cation exchange. While gypsum hydrolysis and sulfide oxidation are the primary producers of SO₄²⁻. Moreover, higher TDS, PH, and degree of cation exchange of geothermal fluids were found in the western part than that in the eastern part. The reservoir temperatures in the eastern and western portions are comparable (115–150 °C). However, the cycle time of the geothermal fluids in the western part (15,743 years on average) is much greater than in the eastern part (2160 years on average), which is considered to be the main reason for the difference in hydrogeochemical characteristics. This study can provide theoretical support for the rational development and usage of geothermal water resources.

Identifying the factors and their interactive effects on soil heavy metals (HMs) accumulation in karst areas is a significant challenge in preventing and controlling soil contamination by HMs. A total of 1043 topsoil (0–20 cm) samples were collected from northwestern Guizhou to determine the concentrations of HMs (Cd, Pb, Zn, Cr, Cu, and Ni). Then, the optimal parameter based geographic detector (OPGD) model was used to identify the driving factors and interactions of natural variables (such as strata, soil organic matter, terrain, etc.) and human activity variables (such as distance from mining sites (DFM), distance from road (DFR), population density (DOP), etc.) on the spatial accumulation of soil HMs in the region. The findings revealed that the average concentrations of all HMs exceeded the corresponding background values of soil in Guizhou Province. Cd had the highest accumulation, followed by Cu, Ni, and Cr. Moran's I and inverse distance interpolation results showed clear clustering trends in the spatial distribution of HMs. The high-high clusters of Cd, Pb, and Zn were concentrated in the northern and southern parts of the study area, while the high-high clusters of Ni, Cr, and Cu were distributed mainly in the eastern and western parts of the study area. OPGD analysis results indicated that soil Cd, Pb, and Zn accumulation was influenced primarily by SOM, DFM, and stratigraphic distribution, followed by pH and soil type. Whereas Ni, Cr, and Cu were mainly affected by stratigraphic distribution. Additionally, DOP, terrain, and soil type were secondary factors affecting the accumulation of these three types of HMs. Notably, the interactive effects among these factors were found to have a more significant impact on HMs accumulation than individual factors alone. Overall, this study provides valuable insights into the main factors influencing the spatial distribution of HMs and their interactive relationships, contributing to the theoretical basis for preventing and controlling HMs pollution in the study area.

Population urbanization significantly influences urban carbon dioxide (CO₂) emissions. As urban areas expand and populations grow, the demand for energy and resources rises, contributing to higher CO₂ emissions. Understanding the objective laws and mechanisms linking these factors is crucial for promoting low-carbon and environmentally sustainable urban practices. This study utilizes the Spatial Autoregressive (SAR) model to explore the impact of population urbanization on CO₂ emissions and innovatively investigates the roles of policies and demographic factors in this process. By examining 30 representative provincial administrative regions in China, the results indicate: (1) From 2000 to 2020, the global Moran's I index for CO₂ emissions generally shows a declining trend, with high-emission areas clustering increasingly in the northern regions; (2) CO₂ emissions exhibit an accelerating upward trend with the progression of population urbanization, with significant regional disparities across eastern, central, and western China; (3) Energy transition policies and the establishment of a carbon emissions trading system are effective in reducing CO₂ emissions; (4) During the process of population urbanization, it is essential to consider urban environmental carrying capacity and employment guidance to ensure a fair energy transition.

Nickel (Ni) and cobalt (Co) are recognized as critical strategic metals by major industrialized nations. In recent years, substantial advancements have been achieved in Ni-Co resource exploration within China, generating a promising prospect for future discoveries. This review provides a comprehensive analysis of significant Ni and Co mineralization events in China, covering metallogenic provinces, deposit types, metallogenic epochs, and associated tectonic settings. Sedimentary Co deposits predominantly formed during the middle Paleoproterozoic (2200–1800 Ma) and early Mesoproterozoic (1600–1400 Ma) ages. In contrast, magmatic Ni-Co and hydrothermal metasomatic Co deposits are concentrated in the early Neoproterozoic (1100–700 Ma) and Paleozoic (220–430 Ma) ages. The intricate correlation between magmatic Ni-Co and hydrothermal metasomatic Co mineralization is linked to the evolution of primitive komatiitic and tholeiitic basalts. The formation of mineralized mafic-ultramafic intrusive rocks is identified as a key factor in the formation of magmatic Ni-Cu sulfide deposits, with the exception of sedimentary Co deposits, which represent a distinct geological event. The primary source of Ni-Co deposits in China can be attributed to a pyroxene-enriched mantle magma source. This is supported by platinum-group element (PGE) characteristics of magmatic Ni-Co deposits, which consistently indicate mineralization associated with partial melting processes within the mantle. Furthermore, sulfur (S) and rhenium-osmium (Re-Os) isotopes in magmatic Ni-Co deposits reveal that crustal materials played a significant role in sulfur saturation during magmatic differentiation and mineralization. Ni-Co resources in China primarily consist of orogenic Ni-Co deposits, intricately linked to the multi-stage orogenic events that shaped the region's geological history. The orogenic Ni-Co system in China exhibits a distinctive profile marked by multi-stage and diversified mineralization. This includes the accumulation of Ni metal through prior mineralization events and the subsequent superposition of Co within pre-existing ore belts, reflecting complex geological processes and interactions. This review aims to contribute to a comprehensive understanding of Ni and Co resources in China, facilitating future exploration and resource management strategies.

The Abiete-Toko Gold District (ATGD), in the Nyong Complex, NW edge of the Congo Craton, is one of the numerous Cameroonian mining districts producing alluvial gold. Although numerous works were focused on the ATGD alluvial gold deposits, their primary source(s) remain(s) unknown. This study combines the chemistry of pyrite and chalcopyrite which were determined by inductively coupled plasma-mass spectrometry (LA-ICP-MS), the chemistry of alluvial gold grains determined by electron probe microanalysis (EPMA), and whole rock composition determined by inductively coupled plasma-atomic emission spectrometry (ICP-AES). The results provide the first evidence of gold in the rocks, and its genesis is subsequently discussed. Gold in the ATGD rocks is essentially invisible and lattice bound in pyrite and chalcopyrite, which intake up to 3.11 ppm and up to 32.6 ppm Au, respectively. The gold-bearing metatexites (garnet migmatite) and ultrabasites (serpentinised peridotites) are here therefore, interpreted as possible sources of the ATGD alluvial gold deposits and occurrences. In metatexite, pyrite and chalcopyrite occur within quartz biotite veins, while in ultrabasites pyrite and chalcopyrite are disseminated grains of millimetric sizes, and ovoid or cubic shapes. Gold mineralisation is shear-hosted and, shows evidence of hydrothermal alteration (sulphidation) induced by circulating magmatic and Co-rich (0.01–1.53 %) fluids.